A comparative study of the CRL-type control charts

Abstract

The CRL (Conforming Run Length) type control charts have attracted increasing interest recently for attribute Statistical Process Control (SPC). The two most promising charts of this type are identified as the CRL-CUSUM chart and the SCRL (Sum of CRLs) chart. This article compares the operating characteristics of these two charts in a comprehensive manner. The general findings reveal that the CRL-CUSUM chart excels the SCRL chart in detecting downward (decreasing) fraction nonconforming (p) shifts and large-scale upward (increasing) p shifts. However, the SCRL chart is superior to the CRL-CUSUM chart in detecting the small and moderate scale upward p shifts, especially when the normal p value is small. The information acquired in this study will provide Quality Assurance (QA) engineers with useful guidance for selecting and applying the CRL-type control charts. Copyright © 2000 John Wiley & Sons, Ltd.